--[[

editor (tentative name) v0.2
by KinoftheFlames

This is an IDE intended to replace the native file editor "edit".
The goal of this program is to make editting lua programs for ComputerCraft as fluid as possible.

For more info: http://www.computercraft.info/forums2/index.php?/topic/4270-wip-in-game-ideedit-program/

CONTROLS:
F3 - Save
F4 - Exit
F5 - Run

CHANGELOG for v0.2:
- Refactored and simplified code to reduce possible errors
- Added message display at the bottom for general information (e.g. program saved, program execution success/failure)
- Added exit without saving confirmation
- Added in-editor program execution (F5)
- Added tab support (more annoying to implement than you'd think...)
- Added page up and page down support
- Changed exit code to return true if exiting normally or false if due to an error

]]

--get filepath
local arg = { ... }
if #arg == 0 then
    print("Syntax: editor <path>")
    error()
end

--debug
local bDebug = false --display debugging info if true
local sDebugText = "" --debug text shown if debugging is on

--settings
local bInsert = true --insert text if true, override text if false
local bShowLineNum = true --toggle visibility of line numbers
local bShowLineNumSep = true --toggle visibility of line numbers seperator
local bShowMessages = true --toggle displaying of messages at the bottom of the screen
local nMinLineDigitsVisible = 1 --[POS] defines how much area for the line numbers is displayed at minimum (program will expand space as needed)
local nSpacesPerTab = 3 --[POS] defines how many visual spaces are in a tab

--flags
local bUnsavedChanges = false --tracks whether the file in the editor has been changed since last saved, helps with exit before saving confirmation
local bConfirmingExit = false --if the user tries to exit without saving, this requires them to try again before succeeding

--variables
local bRunning = true --false when the program exits
local sFilepath = arg[1] --path to the file being editted
local tFile = { } --table of lines for the file being editted
local xMin, yMin = 1, 1 --min values for file display
local xMax, yMax = term.getSize() --max values for file display
local xFile, yFile = 1, 1 --the location of the cursor in the text file
local xScroll, yScroll = 0, 0 --amount file is scrolled on screen
local sMessage = "" --message displayed at the bottom of the screen until next input



------------------------
--    FILE HANDLING   --
------------------------

--load a file from hdd into editor
function load()
    --error handling file
    if fs.exists(sFilepath) then
        if fs.isDir(sFilepath) then
            print("Cannot read directory as a file.")
            error() --exit program
        else
            --load file
            local file = fs.open(sFilepath, "r")
            while true do
                local line = file.readLine()
                if line == nil then --if reached end of file
                    break end

                table.insert(tFile, line)
            end
            file.close()
        end
    else
        table.insert(tFile, "")
    end
end

--save editor's text to a file
function save()
    file = fs.open(sFilepath, "w")
    for i,line in ipairs(tFile) do
        file.writeLine(line) end
    file.close()

    sMessage = "SAVED"
    bUnsavedChanges = false
end



------------------------
--       VISUAL       --
------------------------

--scrolls the screen with the cursor
function scroll()
    alignCursor()
    local x,y = term.getCursorPos()

    if y > yMax then
        yScroll = yScroll + (y - yMax)
    elseif y < yMin then
        yScroll = yScroll - (yMin - y)
    end
    if x > xMax then
        xScroll = xScroll + (x - xMax)
    elseif x < xMin then
        xScroll = xScroll - (xMin - x)
    end
end

--brings the visual cursor to the location of the cursor in file
function alignCursor()
    local charsLeftOfCursor = string.sub(tFile[yFile], 1, xFile-1) --chars left of cursor
    local dummy, numTabs = string.gsub(charsLeftOfCursor, "\t", "\t") --gets the number of tabs

    local x = xMin + (xFile - 1) - xScroll + numTabs * (nSpacesPerTab - 1)
    local y = yMin + (yFile - 1) - yScroll

    term.setCursorPos(x, y)
end

--moves cursor around
function shiftCursor(xShift, yShift)
    --format input for error handling
    if yFile + yShift < 1 then
        yShift = -(yFile - 1)
    elseif yFile + yShift > #tFile then
        yShift = #tFile - yFile
    end


    --handle left/right movement
    if xFile == 1 and xShift < 0 then --if at start of line and moving left, move to end of above line (if exists)
        if yFile ~= 1 then
            xFile = #tFile[yFile-1] + 1
            yFile = yFile - 1
        end
    elseif xFile > #tFile[yFile] and xShift > 0 then --if at end of line and moving right, move to start of next line (if exists)
        if yFile ~= #tFile then
            xFile = 1
            yFile = yFile + 1
        end
    else --horizontal only movement
        xFile = xFile + xShift--normal move
    end

    --handle up/down movement
    if yFile == 1 and yShift < 0 then --if at first line and moving up, move to start of line
        xFile = 1
    elseif yFile == #tFile and yShift > 0 then --if at last line and moving down, move to end of line
        xFile = #tFile[yFile] + 1
    else --vertical only movement
        yFile = yFile + yShift --normal move

        --if the cursor is past the end of the last character after having moved, move it to the last character
        if xFile > #tFile[yFile] then
            xFile = 1 + #tFile[yFile]
        end
    end
end

--move cursor to the start of the line
function shiftCursorHome()
    xFile = 1
end

--move cursor to the end of the line (end of text)
function shiftCursorEnd()
    xFile = 1 + #tFile[yFile]
end

--adjusts borders of editable area depending on settings and situational factors
function applyBoundrySettings()
    if bShowLineNum then
        local chars = #tostring(#tFile) --characters in line num area = num of digits of last line
        if nMinLineDigitsVisible > chars then --unless there is a minimum character count to enforce which is greater
            chars = nMinLineDigitsVisible end
        xMin = chars + 2 --adjust boundry for editable area
    else
        xMin = 1 end
end



------------------------
--      DRAWING       --
------------------------

--redraws entire screen
function draw()
    --clear screen
    term.clear()

    --draw line numbers
    if bShowLineNum then
        drawLineNum() end

    --draw file text
    for i=yMin,yMax do
        if tFile[i+yScroll] ~= nil then --if haven't reached end of file
            term.setCursorPos(xMin, i)
            local modifiedLine = string.gsub(tFile[i+yScroll], "\t", string.rep(" ", nSpacesPerTab)) --replace visual line with defined number of spaces
            term.write(string.sub(modifiedLine, 1 + xScroll, xMax - xMin + 1 + xScroll)) --only draw visible text
        end
    end

    --draw message
    if bShowMessages then
        drawMessage() end

    --draw debug
    if bDebug then
        drawDebug(sDebugText) end

    --place visual cursor in correct position
    alignCursor()
end

--draws line numbers and seperator
function drawLineNum()
    applyBoundrySettings()
    local chars = #tostring(#tFile) --characters in line num area = num of digits of last line
    if nMinLineDigitsVisible > chars then --unless there is a minimum character count to enforce which is greater
        chars = nMinLineDigitsVisible end

    for i=yMin,yMax do
        local lineNum = i+yScroll --line number of file line being drawn
        if tFile[lineNum] ~= nil then --don't draw line numbers for lines that dont exists in the file
            local numSpaces = chars - #tostring(lineNum) --spaces required to right-align numbers

            --draw finally
            term.setCursorPos(1, i)
            term.write(string.rep(" ", numSpaces)) --spaces before line number
            term.write(lineNum) --line number
            if bShowLineNumSep then
                term.write("|") end --seperator --TODO: add customizable line seperator (single char)
        end
    end

    --sDebugText = sDebugText .. " xMin:"..xMin
end

--draw general message at the bottom of the screen for one loop
function drawMessage()
    if sMessage == "" then
        return end

    --add dashes on the side to draw attention
    local openSpace = xMax - #sMessage --openSpace = screenWidth - messageWidth
    local fillerDrawn = (openSpace/2)-1 --dashes drawn on one side of message

    if fillerDrawn < 0 then
        fillerDrawn = 0 end

    if openSpace % 2 == 0 then
        sMessage = string.rep("-", fillerDrawn) .. " " .. sMessage .. " " .. string.rep("-", fillerDrawn)
    else
        sMessage = string.rep("-", fillerDrawn) .. " " .. sMessage .. "  " .. string.rep("-", fillerDrawn) end

    --display message
    term.setCursorPos(1,yMax) --bottom left
    term.write(sMessage)

    sMessage = ""
end

--display debug info in bottom right
function drawDebug(sText)
    term.setCursorPos(xMax + 1 - #sText, yMax) --set cursor at bottom rightmost while still showing all text
    term.write(sText)
end



------------------------
--      DEBUGGING     --
------------------------

--run the program being edited
function run()
    save() --save so its running the program in the editor
    term.clear()
    term.setCursorPos(1,1)
    local success = shell.run(sFilepath)

    --display whether program succeeded or failed, then prompt to continue
    if success then
        sMessage = "SUCCESS - Press any key"
    else
        sMessage = "FAILED - Press any key" end
    drawMessage()

    os.pullEvent("key")
    os.sleep(0) --if the key pressed produces a "char" event, this prevents it from going to the next input loop

    sMessage = "" --clear any messages generated by the run process
end



------------------------
--        OTHER       --
------------------------

--inserts characters the user types in
function insertText(sText)
    tFile[yFile] = string.sub(tFile[yFile], 1, xFile-1) .. sText .. string.sub(tFile[yFile], xFile)
    shiftCursor(#sText, 0)
    bUnsavedChanges = true
end



------------------------
--        CORE        --
------------------------

--intialization
function intialize()
    load() --load file

    --setup screen
    applyBoundrySettings()
    draw()
    term.setCursorBlink(true)
end

--handles user input
function input()
    --wait for key input
    local e, p1 = os.pullEvent()

    --reset exit w/ unsaved changes confirmation if the user presses any other input than exit
    if bConfirmingExit == true and e == "key" and p1 == keys.f4 then
        exit()
    else
        bConfirmingExit = false end

    if e == "char" then --handles character input
        insertText(p1)
    elseif e == "key" then -- handles non-character input
        --DONT USE F2, F10, F11, ALT, ESC

        --functional keys
        if p1 == keys.f1 then --menu

        elseif p1 == keys.f3 then --save
            save()
        elseif p1 == keys.f4 then --exit
            exit()
        elseif p1 == keys.f5 then --run program in editor
            run()

        --arrow keys
        elseif p1 == keys.up then
            shiftCursor(0, -1)
        elseif p1 == keys.down then
            shiftCursor(0, 1)
        elseif p1 == keys.left then
            shiftCursor(-1, 0)
        elseif p1 == keys.right then
            shiftCursor(1, 0)

        --home, end, page up, page down
        elseif p1 == keys.home then --home
            shiftCursorHome()
        elseif p1 == keys["end"] then --end
            shiftCursorEnd()
        elseif p1 == keys.pageUp then --pasge up
            shiftCursor(0, -(yMax-yMin))
        elseif p1 == keys.pageDown then --page down
            shiftCursor(0, yMax-yMin)

        --backspace, delete
        elseif p1 == keys.backspace then --backspace
            if not (yFile == 1 and xFile == 1) then --if not at the first character in the file
                if xFile == 1 then --if at the start of a line, concatenate line above with this line
                    shiftCursor(0,-1)
                    shiftCursorEnd()

                    tFile[yFile] = tFile[yFile] .. tFile[yFile+1] --concat lines
                    table.remove(tFile, yFile+1) --remove second line
                else --otherwise just delete one character
                    shiftCursor(-1,0)
                    tFile[yFile] = string.sub(tFile[yFile], 1, xFile-1) .. string.sub(tFile[yFile], xFile+1)
                end
                bUnsavedChanges = true
            end
        elseif p1 == keys.delete then --delete
            if not (yFile == #tFile and xFile == #tFile[yFile] + 1) then --if not at the last character in the file
                if xFile > #tFile[yFile] then --if cursor is at the end of the line, concatenate with line below
                    tFile[yFile] = tFile[yFile] .. tFile[yFile+1] --concat lines
                    table.remove(tFile, yFile+1) --remove second line
                else --otherwise just delete one character
                    tFile[yFile] = string.sub(tFile[yFile], 1, xFile-1) .. string.sub(tFile[yFile], xFile+1)
                end
                bUnsavedChanges = true
            end
        --enter, tab
        elseif p1 == keys.enter then --enter
            if xFile <= #tFile[yFile] then --if cursor is between characters
                table.insert(tFile, yFile+1, string.sub(tFile[yFile], xFile)) --move remainder of characters to a new line
                tFile[yFile] = string.sub(tFile[yFile], 1, xFile-1) --and delete the moved characters from the previous line
            else --cursor at the end of the line
                table.insert(tFile, yFile+1, "")
            end
            shiftCursorHome()
            shiftCursor(0,1)
            bUnsavedChanges = true
        elseif p1 == keys.tab then --tab
            insertText("\t")
            bUnsavedChanges = true
        end
    end
end

--main loop
function mainLoop()
    while bRunning do
        --clear debug info
        sDebugText = ""

        input() --get input and respond

        --debug info
        local x,y = term.getCursorPos()
        sDebugText = sDebugText .. " File:"..xFile..","..yFile .." Scrn:"..x..","..y

        scroll() --shift screen to show cursor
        draw() --update screen
    end
end

--exit program
function exit()
    if bUnsavedChanges and not bConfirmingExit then --if there are unsaved changes, and this warning hasnt displayed yet
        sMessage = "UNSAVED CHANGES - Press F4 to exit"
        bConfirmingExit = true
    else
        bRunning = false end
end

--have the program exit cleanly and tidily
function exitCleanup()
    term.clear()
    term.setCursorPos(1,1)
end

intialize()
mainLoop()
exitCleanup()